Two-cycle engine, crankcase compression, valve piston



DCC. 2, 1947. R, L FISHER 2,431,859

Two CYCLE ENmNE, cRNKcAsE coMPREssIoN, `VALVE: VPIsToN FiledtJune-zs, 1945 3 Sheets-Sheet 1 R. J, FISHER Dec. 2, 1947.

TWO CYCLE ENGINE,' CRANKCASE AGOMPRESSLON, VALVE PISTON 5 Sheet-s-Shet 2 Filed June 28, 1945 R. J. FISHER 2,431,859 I Dec. 2,'1947.

TWO CYCLE ENGINE, CRANKCASE COMPRESSION, VALVE PISTON `Filed June 28, 1945 3 Sheets-Sheet 3 l nq. 6. Fig,

Patented Dec. 2, 1947 TWO-CYCLE ENGINE, CRANKCASE COMPRESSION, VALVE PISTON Reginald John Fisher, Leamington Spa, England Application June 28, 1945, Serial No. 602,081 In Great Britain July 14, 1944 8 Claims.

This invention relates to internal combustion engines working on the two-stroke cycle, and has for its object to provide a two stroke cycle engine in which only the exhaust ports are controlled by the movement of the piston, the transfer of the precompressed charge from the crank chamber or precompression pump into the cylinder taking place through a valve which does not depend for its opening on the position of the piston.

According to the invention the precompressed charge enters the cylinder through a port situated in the piston head and controlled by a valve closure member guided for free movement between its seat and movement limiting means, the opening force on the valve due to excess of pressure on the side remote from the cylinder being unopposed except by forces due to the inertia of the valve closure member itself.

The valve closure member is preferably so balanced that there are no inertia forces acting on it in the direction of its opening and closing movement. The piston head may be provided with a conical guiding surface which, when the valve closure member is oli its seat, co-operates therewith to direct the charge towards the centre of the cylinder head, and helical Vanes may be provided at at least one side of the valve closure member to give a whirling motion to the charge passing through the port. A part of the piston head may be formed to a shape closely corresponding to that of the cylinder head, this part of the piston head being arranged to approach closely to the cylinder head so as to produce turbulence of the charge.

The invention is 4hereinafter described with reference to the accompanying drawings, in which:

Fig. 1 is a sectional elevation of one form of single cylinder air cooled internal combustion engine according to the invention, the section being in the plane of the axis of the crankshaft;

Fig. 2 is a section at right angles to Fig. 1 of a similar, but slightly modied engine;

Fig. 3 is a fragmentary section through the piston of an engine showing a, modied valve arrangement;

Figs. 4 and 5 areviews similar to Fig. 3 showing other modified arrangements;

Figs. 6 and '7 show further modified valve arrangementsincorporated in engines of the watercooled type; and F Fig. 8 is a transverse section on the line 8-8 of In the form of engine shown in Fig. l the piston 3 which is coupled to a crankpin 9 on a crankshaft 9a by a connecting rod I, is formed with a central recess II in its crown, the side walls I2 of which converge towards the mouth of the recess. In the base of the recess is a large coaxial port I3 leading through to the underside of the piston, and the base of the recess around the port I3 provides a seat I4 for a valve closure member I5 in the form of a flat disc to which is secured a stem I. The disc s smaller in diameter than the recess. A boss iI in the centre of the port I3 is supported by radial arms I8 which may, as shown in Fig. 2, take the form of helical vanes, and the stem I5 of the valve closure mem,- ber passes through the boss. A collar I9 on the lower end of the stern limits the upward movement of the valve closure member, and a spring 20 housed in the boss acts to urge the valve closure member towards its open position.

The part 2I of the piston head surrounding the recess II is shaped t0 conform closely to a registering part 22 of the cylinder head, and approaches closely to the cylinder head as the piston reaches its top dead centre position, thus forcing the charge in the cylinder to move radially inwardly, and producing turbulence. A ring of exhaust ports 23 is formed in the cylinder wall, and is uncovered by the piston 8 as it approaches its bottom dead centre position.

The operation of the engine is as follows:

VAssuming that the piston 8 is at the top dead centre position and a charge in the cylinder has just been ignited, the pressure above the piston is much greater than the pressure below and the valve disc I5 is held on its seat.A The piston 8 is vflows into lthe cylinder, being directed upwardly towards the centre of the cylinder head by the convergent walls I2 of the recess II. The remaining spent charge is thus directed towards the walls of the cylinder and downwardly towards the exhaust ports 23, and no substantial mixing of the new charge with the spent charge takes place.

' A point is reached when the pressures above and below the piston are equalised, and the valve disc l5 closes. When the' piston 8 passes its bottom dead centre position and begins to move upwardly the exhaust ports 23 are closed and the charge in the cylinder begins to be compressed, so that there is again a pressure difference holding the valve disc 23 closed. The charge is thus compressed during the upward stroke of the piston 8, until the top dead centre position is reached, the charge ignited as by the sparking plug 24 and the cycle repeated. A f

The var-iesVI I8 tend to produce' aifwhirling motion of the charge, thus tending to set up a vortex in the cylinder, and the exhaust ports may be tangential or inclined to the radial direction in such a direction that the vortical motion-assistsfthe flow of the exhaust gases into them.-v '1 i With the arrangementaboveidescribed the inertia of the valve disc I tends to seat it during the deceleration of the pistonrasfits approaches its bottom dead centre, and the acceleration-:as it commences its upward stroke. As the-pressure diierence between thel upper and lower sides of the rpistonflvis not Veri/ great at this time, this inertia .effect would tend to'close theV port before the full charge was'transferred to the cylinder. 'To`avoidthis, the valve disc I5 is lightly loaded by the. spring 'Z5 toWar-dsits 'open' position.

The spring `2D 'may' be omitted, andthe Vvalve Adisc I 5 counterweighte'd as'shown in Fig. 3, one or (more counterweights A25 beingmounted in guiding. recesses 26 in the underside of the pistonand .leversr40.. y In thefarrangementshown in11:Fig\. "I,' the ring is open. The charge, passing between the inclined surfaces of the ring and boss, is directed inwardly and upwardly towards the centre of the cylinder head. The ring 35 is counterbalanced by an annular weight 38 sliding on a reduced portion 39 of the boss 33, and coupled to it by radial 35 Which'forms the valve member is of the full diameter of the piston 3, and may be provided with piston rings 4| making it a gas-tight t in 'fthe cylinder, fan internal coned face 42 on the ring-35 mating with a coned surface 43 on a cen- ,tral-boss44 -on.the1piston, as described in the being coupled to the valve-disc.by levers `2"I""piv ot'ed at"28.

-"Fig-4 shows anarrangement 'inwhichthe valve 'closure member I5 is a plain disc guided` byi'ibs 29 projecting from thewalls of -recess vII,a'nd having its opening limited by set screws 3E) extending obliquelythrough the piston head. The ribs`29 may lbe of helical' formv a's shown, to 'create a whirling motion ofthe' charge.

`In the arrangement showni'nfFig. 5, the valve disc I5 is annular inform, .and 'co-operateswith anannular port inthe' piston head. /In this arrangement, the sides ofthe recess I I inthe piston head are parallel; the outer edge of thevalve disc I 5.ttingrelativelyclosely therein;andthe 'charge 'fiowingpast its inner edge, Lto 'be-deecte'd'up- Hwardlyby a conicalboss v3| '.inithe centre of the ...recess In this.arrangement,;theopening ofthe valve discis'limited by a'spring ring -4'Ilocated' in a 'groove in the wallofthezrecess YI I.

The valve closure memberneednot bearrang'ed in a recess in the"piston 'head, Y but .maybe subfstantially vin the plane '.of `the piston 'head surjface when closed, ,the;jcylinder,head'being vso jfformedthatlit is 'recessed 'opposite to thepa'rt of .thepiston'lhea'd which carries,`theivalve. HTwo arrangements of this kind 'are vshown in Figs. 6 and 7, the Vcylinderhead in Fig. '6 being'formed `with a, central recessandthe valve member beinglocated in the centre of the` piston, or as shown in`Fig.`7,lthe valve member may'be annular "and .surround acentralpar'toflthe piston. the valve imemberforming a substantialpart of the'head of ther'iis'ton.v I

,Inthe arrangementshowninfFigsf and 8, the

wall portionLlSI., .The upper part of the .ring 35 has itsjnclinedsuraceL3'I oppositeto the coned .upper end `34 0f.`the .boss 33,'so .`that when the ,said inclined surface 31 rests fon the 'boss the 'passage .through 'the piston fis: closed, f and Vwhen the ring is lifted, the passagef'through`thcfpi-ston immediately proceeding example. In this case the -valve member35sis balanced by a counterweight 145 mounted inside the boss 44 and connected to thezvalve member by levers 46. In this latter arrangement, the valve member forms a substantialpart of -the piston head.

The invention mayibe applied to a double-acting. engine, a valveV bein'garranged' in each of' the working faces of thepisto'mthe appropriate valve Opening automatically to admit a' charge t0 either end ofthe cylinderwhenthe pressure conditions are'suit'able.

'In engines in'which the charge is precompressed by means other than the descent of the piston towards the crank chamber, the charge may be delivered to a circumferential series of ports around thecylin'derbelow the exhaust ports in "'the'pist'o'n whenthelatter is vat or near its bot- *tom dead' centre position. The ports in the' piston lead intoa vchamber inthe piston, which chamber is'connec'ted'bya port, controlled'by the valve closure 'member'accordingto the invention,

to', the upper side of thefpiston.v

by thepiston as it approaches its bottom dead 4centre position, a port Ysituated in the piston head toftransmit,aiprecompressed.charge to the cylyinder, :a valve seat, .a =valve closure member cooperating with saidseat; for closing said port, .movement limitingmeanss limiting'the opening of said valve closure member, `and'means which :act upon .the valveclosure member'to oppose'the .closingforce thereon ldu'efto the inertia'of -said member, during deceleration of the piston appreaching the bottom vdead center 'position yand 'acceleration-of the piston leaving lthe bottom vdead centerposition', thefopening and closing of said Vvalve closure member being controlled by pressure differences on'itsitwo sides.

A2..,In ai two fstrokecycle internal combustion engine, .acylinden apiston reciprocable in said cylinder, exhaust/ports in said 'cylinder exposed by .the piston as itapproaches its bottom dead centre position, affp'ort 'situated in the piston headto transmit 'apre-compressed charge tothe cylinder, afvalve "seat, a. valve 'closure member eo-'operating withsaid'seatfor 'closing saidxport, movement limiting means limiting the opening "of said valve 'closure member, and balancing means connected to said valve closure member 'tobalance the inertia'for'c'es 'actingthereom said valve closure member being controlled solely by pressure differences on its two sides.

3. In a two stroke cycle internal combustion engine, a cylinder, a piston reciprocable in said cylinder, exhaust ports in said cylinder exposed by the piston as it approaches its bottom dead centre position, a port situated in the piston head to transmit a precompressed charge to the cylinder, a valve seat, a valve closure member co-operating with said seat for closing said port, movement limiting means limiting the opening of said valve closure member, a conical guiding surface on said piston head, said valve closure member being movable freely between the seat and the position defined by said movement limiting means and in the latter position co-operatin-g with the conical guiding surface to direct the charge towards the center of the cylinder head, and means which act upon the valve closure member to oppose the closing force thereon due to the inertia of said member, during deceleration of the piston approaching the bottom dead center position and acceleration of the piston leaving the bottom dead center position, the opening and closing of said valve closure member being controlled by pressure differences on its two sides.

4. A two stroke cycle internal combustion engine according to claim 2, wherein the valve closure member is counterbalanced by a mass or masses mounted in the piston for movement in the direction of reciprocation of the piston and connected to the valve closure member by a lever or levers.

5. A two stroke cycle internal combustion engine according to claim 2, wherein the valve closure member is annular and has an internal conical face seating on a convex conical face on the piston.

6. A two stroke cycle internal combustion engine according to claim 2, wherein the valve closure member is annular, has an internal conical face seating on a convex conical face on the piston, and is counterbalanced by a co-axial Weight which it surrounds, and to which it is connected by levers.

7. A two stroke cycle internal combustion engine according to claim 2, wherein the valve closure member is annular, has an internal conical face seating on a convex conical face on the piston, is of the full diameter of the piston, and is provided with piston rings making it a gastight iit on the cylinder.

8. In a two-stroke cycle internal combustion engine, a cylinder, a piston reciprocable in said cylinder, exhaust ports in said cylinder exposed by the piston as it approaches its bottom dead center position, a port situated in a recess in said piston head to transmit a precompressed charge to the cylinder, a valve seat, a valve closure member cooperating with said seat for closing said port, movement limiting means limiting the opening of said valve closure member, an annular surface on said piston surrounding the recess therein, a surface in the cylinder head conforming substantially in shape to said annular surface and adapted to be approached closely by said annular surface to produce turbulence of the charge, and means which act upon the valve closure member to oppose the closing force thereon due to the inertia of said member, during deceleration of the piston as it approaches the bottom dead center position and acceleration of the piston as it leaves the rbottom dead center position, the opening and closin-g of said valve closure member being controlled by pressure diierences on its two sides.

REGINALD JOHN FISHER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 741,559 Smith Oct. 13, 1903 803,078 Thompson Oct. 31, 1905 1,010,754 Hall Dec. 5, 1911 1,107,501 Duryea Aug. 18, 1914 1,333,635- Sawtelle Mar. 16, 1920 1,413,912 Harper Apr. 25, 1922 FOREIGN PATENTS Number Country Date 4,443 England 1912 

